This project focuses on a specific subgroup of immune cells—memory B cells—that may play an important role in MS. The team previously found that higher levels of a marker called FCRL5 in the fluid around the brain and spinal cord can predict the occurrence of new brain lesions. Now they will study these FCRL5-positive B cells in detail—their abundance, localization, function and whether genes or certain viral exposures influence them—with the aim of turning this into a useful biomarker to follow disease activity and response to treatment.